In the field of lighting, light-emitting diodes (LED's) are becoming more and more popular because they are advantages as being compact, high-efficiency, durable and diverse in colors. Unlike conventional lighting elements, an LED lamp generally comprises a plurality of LED ships arranged in an array because a single LED ship is small and emits light of relatively insufficient intensity. Moreover, the light from an LED is directional. In an LED lamp, the LED chips are usually arranged inclined or are provided with light control elements to meet the requirements of a candela distribution curve. However, it costs higher when the LED chips are arranged inclined because additional molds are required and the assembly cost rises, which leads to higher cost and lower popularity of the LED lamp. Moreover, the use of light control elements reduces the light-emitting efficiency, which can be compensated by increased numbers of LED chips with more electricity consumed and higher lamp cost.
Conventionally, to meet the requirements of a candela distribution curve, the LED lamp uses light control elements such as light control lenses, geometrical reflecting screens and LED devices that are arranged to correct the candela distribution curve of the LED lamp.
U.S. Pat. Pub. No. 2006/0232976 discloses a lighting device with an integration sheet as shown in FIG. 1. The lighting device comprises a light source 21 and at least a sheet 22. The light source 21 comprises a luminous body 211 and a reflecting screen 212. The sheet 22 is disposed at the light-emitting end of the light source 21. The sheet 22 comprises a plurality of light diffusion zones 221, 222, 223. Each of the light diffusion zones 221, 222, 223 has a plural arrays of microstructures arranged on the surface thereof and each array of microstructures is capable of changing the diopter of the corresponding light diffusion zone. By controlling the distribution of the plural arrays of microstructures, the Gaussian distribution of the light source 21 can be improved while collimating the scattered light beams to the intended illuminating area 9 of the lighting device and diffusing the light beams emitting from the center of the light source 21 to the same so that not only the luminous efficacy of the lighting device is enhanced, but also the uniformity of the illuminance of the lighting device is improved.
U.S. Pat. Pub. No. 2006/0139933 discloses a reflector with negative focal length as shown in FIG. 2. The top of the luminaire screen 20 is a reflector of single negative focal length 51, such that the cross section of the luminaire screen 20 is a concavity with a side screen 52 connecting to the edge of the reflector 51. By the luminaire screen 20 of FIG. 2, the upward-incident rays emitting from a light source 53 are first reflected to the side screen 52 by the reflector 51, and then are further reflected such that a plurality of discharging rays 54 are generated. It is noted that the discharging rays 54 are discharge out of the luminaire by large angles for reducing glare. In addition, the height of the luminaire can be reduced.
U.S. Pat. No. 5,838,247 discloses a solid state light system as shown in FIG. 3. In FIG. 3, a lamp 40 has a plurality of inclined lamps 12 with a reflector 44 inclined at a complementary angle A, so as to direct the light parallel to the polar axis 36 of lamp 40. The angle of convergence or divergence may vary, with the angle of the reflector correspondingly selected to achieve the desired direction and type of light output.